1. Field of the Invention.
This invention generally relates to optical connectors, and more particularly to an optical fiber guide module for aligning one or more fibers to an optical or opto-electronic chip and a method for making an optical fiber guide module of this type.
2. Description of the Related Art.
Because of their high transmission speeds and wide bandwidth, fiber-optics has become the preferred technology in communications networks, both domestically and abroad. The switch to this technology has necessitated an upgrade in the connectors which optically couple signal fibers to other elements of a system. For example, it has become the recent trend to replace electronic integrated circuits with optical or opto-electronic chips. This replacement has not only increased signal transmission and processing speeds, but also has increased integration density.
U.S. Pat. No. 5,631,988 to Swirhun discloses a conventional fiber-optic connector. This connector includes an element (often referred to as a block or a holder) for securing an array of optical fibers. The holder is mounted on a substrate using mechanical alignment pins. A connection is then established between the fibers and circuitry on the substrate to complete the assembly. U.S. Pat. Nos. 6,056,448, 5,590,232, and 5,420,954 disclose similar connectors.
Conventional connectors of the aforementioned type have proven inefficient in a number of ways. First, their size has frustrated attempts towards miniaturization. This is attributable mainly to their use of an optical-fiber holder as an element separate from the substrate. The optical-fiber holder also limits the number of connections to the substrate, and the use of mechanical pins to align the holder with the substrate has also increased size.
Other known connectors attach an optical fiber to an optical chip via a separate flexible substrate. U.S. Pat. No. 5,774,614 discloses a connector of this type. One of the main disadvantages of this connector is that the flexible substrate adds to the size of the connector, thereby preventing miniaturization. This connector is also undesirable because automatic alignment machinery must be used to align the chip with the fiber.
In view of the foregoing considerations, it is clear that conventional fiber-optic connectors are too large, too expensive, and require far too many process steps for their manufacture. In order to meet the ever-increasing demand for smaller and faster optical systems, optical connectors must be improved in terms of their size, speed, and performance.
A need therefore exists for a connector, or connector module, which couples optical fibers to one or more optical or opto-electronic chips using fewer parts than conventional connectors, while at the same time increasing the number of fiber connections. Such a module will have increased integration density and functionality, thereby increasing the size and signal transmission speed of the optical systems into which they are incorporated.
It is a first object of the present invention to provide an optical fiber guide module which is smaller in size, achieves a greater number of fiber-optic connections, and thus has improved integration density over conventional connectors.
It is another object of the present invention to achieve the first object by integrating an optical-fiber holder of the guide directly into the substrate on which one or more optical or opto-electronic driver chips, amplifiers, and modulator chips are mounted, and more specifically by eliminating the use of a holder as an element separate from the substrate, thereby allowing the fiber guide of the invention to achieve a size which is substantially smaller than conventional connectors.
It is another object of the present invention to provide an optical fiber guide of the aforementioned type which connects a greater number of optical fibers than are connected by conventional connectors, which have only a limited number of connections as a result of their use of an optical-fiber holder.
It is another object of the present invention to provide an optical fiber guide module which optically couples optical fibers to one or more optical chips using flip-chip technology, thereby eliminating the need for mechanical alignment pins and thus further increasing integration density and the ability to miniaturize the overall optical system.
It is another object of the present invention to provide an optical fiber guide which includes a substrate made of a material with a coefficient of thermal expansion the same or similar to that of the optical chip, thereby ensuring that the optical fibers and optical chip remain in alignment regardless of temperature variations or other external thermal influences.
It is another object of the invention to provide an optical fiber guide which attaches an optical chip directly to a multi-functional ceramic substrate, thereby removing the need to use automatic machinery to align the chip and fibers, and instead using far more efficient flip-chip solder techniques for this purpose. Attaching the optical chip directly to a multi-functional substrate also promotes miniaturization, a goal which is frustrated by many conventional designs which mount the optical chips to be connected to a separate substrate or printed circuit board. This direct-attach design improves performance with respect to speed, power efficiency, and noise.
It is another object of the present invention to provide a method for making an optical fiber guide using fewer steps than required by conventional methods.
The foregoing and other objects of the invention are achieved by providing a fiber guide which functions as an optical-fiber holder integrated directly into a substrate on which an optical chip is mounted. This is achieved by forming one or more holes in the substrate either by lithography or molding techniques. Preferably, the substrate has a multi-dimensional matrix of holes to thereby maximize the integration density and number of connections sustainable by the fiber guide. The substrate, thus, functions both as a guide for the optical fibers as well as a carrier for the optical chip.
To reduce the need for alignment pins, the fiber guide of the invention uses, in accordance with one embodiment, flip-chip soldering techniques to mount the chip onto the substrate at a position where the optical receivers and/or transmitters of the chip are aligned with the optical fibers. Flip-chip techniques are especially desirable when the optical chip has multiple light transmitting and receiving ports, since the surface tension between the solder bumps on the optical chip and substrate will bring these optical devices into alignment with the matrix of holes. Alternately, a conductive adhesive may be used to connect the optical chip to the substrate.
Preferably, the substrate is made of a material having a coefficient of thermal expansion which is substantially similar to the coefficient of thermal expansion of the optical chip. This will advantageously allow the chip and substrate to expand and contract in unison, thereby preserving optical coupling between the fibers and optical chip regardless of external temperature influences. The integration density of the modularized fiber guide junction of the invention may be further enhanced by mounting one or more integrated chips onto the substrate. The back of the substrate may be equipped with metallic alignment pads for attachment to a board, card, module, or other circuit connections. To further increase the functionality of the invention, the substrate may be equipped with one or more guide holes for connecting power and/or ground lines to the optical chip.
The method of the present invention has fewer process steps than conventional methods because the optical fiber guide of the invention as comparatively fewer parts. This method includes forming one or more holes in a substrate, mounting an optical chip on a first side of the substrate at a position which aligns an optical receiver and/or transmitter of the chip with the hole or holes in the substrate, and connecting one or more optical fibers to the hole or holes in the substrate.